NEWS & PRESS

Gravitational waves were predicted by Einstein's general theory of relativity, published in 1916. However, although astronomers have indirect evidence of their existence, none have yet been detected directly.

UK scientists are at the forefront of the search for these elusive ripples in spacetime, with involvement in two ground-based experiments: the UK/German GEO 600 project and the US LIGO experiment (Laser Interferometer Gravitational-Wave Observatory).

Now, UK industry has also been given a major role to play. On Wednesday, 23 June, EADS Astrium in Stevenage will be awarded the contract for the LISA Pathfinder spacecraft by the European Space Agency (ESA).

"Whilst EADS Astrium has led most of ESA's space exploration projects over recent years, such as Rosetta, Mars Express and Venus Express, this is the first Space Science contract for many years to be primed from the UK," said Dr. Mike Healy, UK Director for Earth Observation, Navigation and Science, EADS Astrium.

"It's a fantastic opportunity for our team at Stevenage and follows on from similar recent successes like Aeolus, an Earth Science project to provide global measurements of wind speed, and Galileo, Europe's satellite navigation system."

LISA Pathfinder is a demonstration mission that is designed to test the advanced technologies required by the ESA-NASA Laser Interferometer Space Antenna (LISA), a complex, multi-spacecraft mission that is scheduled for launch in the first half of the next decade.

Over a period of at least 2 years, LISA will detect gravitational waves from a variety of compact objects, ranging from massive black holes at great distances from the Earth to sub-solar mass white dwarfs - extremely dense, glowing remnants of dead stars - in our Galaxy.

The mission will consist of three spacecraft flying 5 million kilometres (3 million miles) apart in an equilateral triangle formation. Laser beams traveling between the spacecraft will be reflected from two test masses in each satellite. By obtaining extremely accurate measurements of the distance between the spacecraft, it will be possible to determine whether the fabric of spacetime in which they are traveling has been distorted by passing gravitational waves.

The formation of 3 spacecraft will face the Sun and lie in a plane that is tilted at 60 degrees to the Earth's orbit. The trio will orbit the Sun following 20 degrees behind the Earth, and will rotate once per year. This orbital motion will help to detect the direction of each source of gravitational radiation.

Although LISA will not be affected by vibrations found in ground-based observatories, the test masses must be cocooned within active shields to protect them from the constant buffeting by charged particles pouring out of the Sun. Sensors will detect the relative motion of the spacecraft and the delicate test mass mirrors, and will command thrusters to minimise the relative motion.

In order to prepare for this challenging mission, ESA will first test the drag-free and laser-sensing technique on the LISA Pathfinder mission, which will be developed over the next few years. Pathfinder will consist of a single satellite containing two freely flying test masses just like those in LISA, together with a precision laser distance measurement system to monitor the motion of the masses.

Novel micro-thrusters will be used to control spacecraft motion and actively shield the test masses. The aim is to be able to position the spacecraft to the nearest nanometre (billionth of a metre) with respect to the masses, and to demonstrate that they are following purely inertial trajectories, unperturbed by external forces. LISA Pathfinder will also carry a similar test package from NASA called ST-7.

"The observation of gravitational waves from violent astrophysical sources in the Universe is one of the most challenging problems for experimental physics, " said Professor Jim Hough (University of Glasgow). "As this provides a new window on the Universe the potential rewards for fundamental physics and astrophysics are enormous."

Several research groups in the UK are involved in research for both LISA and LISA Pathfinder. They include the Universities of Glasgow and Birmingham, Cardiff University, Imperial College and Rutherford Appleton Laboratory (CCLRC). The UK Particle Physics and Astronomy Research Council (PPARC) is providing £3.5M specifically to develop the instrument, known as the LISA Technology Package, for LISA Pathfinder.